# How does changing the percentage of sucrose added to yeast affect the rate of respiration of yeast as measured by the height of gas bubbles (froth) ?

by lizzielunn817gmailcom (student)

Biology Internal Assessment

DCP and CE

“Frothy Yeast”

2014

Research Question

How does changing the percentage of sucrose added to yeast affect the rate of respiration of yeast as measured by the height of gas bubbles (froth) achieved above the yeast-sucrose suspension in 360 seconds?

Raw Data table showing the effect changing the percentage of sucrose added to yeast has on the rate of respiration of yeast as measured by the height of gas bubbles (froth) achieved above the yeast-sucrose suspension in 360 seconds.

Observations

• The temperature of our water bath was 42 not 40 as programed
• When pouring the yeast into the tall test tubes it smeared the sides
• The cylinders rested in the water bath at an angle
• The height of the froth was uneven at different points around the test tube.
• In the 0% experiment very small bubbles formed
• There were water droplets on the inside of the cylinder after washing
• It was difficult to wash the test tubes

Processed Data Table 1 showing the effect changing the percentage of sucrose added to yeast has on the rate of respiration of yeast as measured by the rate of gas bubbles (froth) produced by the yeast above the yeast-sucrose suspension in 360 seconds.

Processed Data Table 2 showing the effect changing the percentage of sucrose added to yeast has on the rate of respiration of yeast, as measured by the mean rate of gas bubbles (froth) produced by the yeast above the yeast-sucrose suspension in 360 seconds and the standard deviation from the mean.

Example:

From -

Graph showing the effect changing the percentage of sucrose added to yeast has on the rate of respiration of yeast, as measured by the mean rate of gas bubbles (froth) produced by the yeast above the yeast-sucrose suspension in 360 seconds and the standard deviation in the form of error bars from the mean.

Comment on the graph:

The calculated standard deviation and error bars are for three of my results (0%, 10% and 15%) were small, indicating that these the values were close to the mean and therefore valid.  However at 5% sucrose, the error bar is very large (1SD is 0.028 mm) this indicates that the values recorded for this percentage was less valid and some other factor may have been affecting the results. This error bar also overlaps the 3 other data points (10%, 15% and 20%) this indicates that there may be no clear trend due to this overlap. The error bar for 20% is also large, indicating that it was not very valid. The curve of best fit is reasonably accurate and it passes through all of the error bars. This indicates that the trend indicated by the curve is accurate.

Conclusion:

In my experiment I investigated whether changing the percentage of sucrose added to yeast affects the rate of respiration of yeast as measured by the height of gas bubbles (froth) achieved above the yeast-sucrose suspension in 360 seconds.

From my results I can infer that changing the percentage of sucrose does affect the rate of respiration of yeast. At first as there is a steep increase in the amount of CO2 produced and thus the rate of the froth produced, when we increased the concentration of sucrose from 0% to 5%. However after this point there is a ...